1. Field of the Invention
The invention generally relates to an optical beam splitter/coupler, and more particularly relates to a planar waveguide diffraction 1xc3x97N beam splitter/coupler fabricated by an integrated circuit manufacturing process.
2. Related Art
In recent years, the wavelength division multiplexing (WDM) method has been widely used in fiber optic communication systems. 30 or more channels carrying light beams of different wavelengths are used to transfer data so as to increase the information carrying capacity. To fulfill the demand of increasing transference capacity, a structure of dense wavelength division multiplexing (DWDM) is being developed to increase the density of the transmission channel and create a high capacity, wide band fiber optic communication system. In a DWDM system, a plurality of information carrying light beams of different wavelengths are combined (coupled or multiplexed) onto a single fiber to increase its information carrying capacity through the optical fiber. At the receiving end, the beams are spatially separated (split or demultiplexed) and each beam is received by a separate detector for recovery of the information that it carries. Current common techniques for beam splitting coupling are fused fiber and ribbed waveguide. The fused fiber is easy to fabricate but inadequate for beam splitting because it has fewer channels, bulky dimensions and unsatisfactory component integration. On the contrary, the waveguide coupler has better beam splitting, more channels, less dimensions and better component integration, but is relatively difficult to fabricate and is less flexible in assembly applications.
The previous beam splitters and couplers have the disadvantages of higher energy loss and higher fabrication cost. Especially when fabricating a 1xc3x97N/Nxc3x971 beam splitter/coupler, it requires a plurality of 1xc3x972/2xc3x971 beam splitters/beam couplers linking serially, which loses a great deal of transmission energy.
U.S. Pat. No. 4,953,935 by Suchoski, Jr., et al. entitled xe2x80x9cIntegrated Optic Star Couplerxe2x80x9d and issued Sep. 4, 1990 discloses an optical coupler including a planar substrate for receiving a circuit array of one or more surfaces for splitters disposed thereon by a two step proton exchange (TSPE) process. Although the optical coupler is fabricated through a semiconductor process, it still has the disadvantages of higher waveguide loss and coupling loss.
U.S. Pat. No. 4,274,706 by Tangonan, et al. entitled xe2x80x9cWavelength Multiplexer/demultiplexer for Optical Circuitsxe2x80x9d and issued Jun. 23, 1981 discloses a wavelength selective coupler that comprises a planar optical waveguide formed within a glass substrate having an input/output surface at one end and a curved surface at the other end upon which is mounted a reflective diffraction grating. The periodic diffraction grating acts as a demultiplexer. The grating is a separate unit adhered to the curved surface that is formed on one end of the waveguide. The input/output surface formed at the other end of the waveguide is a polished flat surface. The fabrication processes for the curved surface and the flat surface and adhering of the grating are rather complicated and difficult.
The object of the invention is therefore to provide a beam splitter/coupler, which is easy to fabricate, small in size and more flexible for applications.
To achieve the aforesaid object, a beam splitter/coupler according to the invention utilizes a Fourier transform diffractive optical element (DOE). The surface of the diffractive optical element is designed to diffract an incident beam into several (N=number of) beams with the same intensity. The invention further applies fabrication techniques of the planar waveguide to form a Fourier transform diffractive optical element on one end of the planar waveguide. For example, a micro-etching process for the mask of the integrate circuit can be applied for fabricating a beam splitter/coupler with a Fourier transform diffractive optical element formed on a planar waveguide.
Further scope of applicability of the invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.